This invention relates to the repair of worn or damaged areas of cylinders and, in particular, to the repair of cylinder walls without necessarily changing the bore dimensions thereof.
As modern technology gets more complex, the machines that result therefrom correspondingly increase in complexity and expense. In addition, in recent years there has been a tendency for this modern technology to be introduced all over the populated world. The foregoing factors have contributed to the adoption of standardized parts as an accepted practice in machine design. This is for a variety of reasons. For example, the use of standardized parts leads to decreased unit cost. Additionally, repairs are simplified because replacement parts need not be modified if they conform to the standards set for that part. Still further, the distribution of parts is simplified since only a limited number of parts need be stocked. This latter factor is significant when it is considered that many complex machines may be in rather remote parts of the world.
The foregoing is especially significant in the case of airplanes which fly to all parts of the world and are subject to severe stresses and normal wear that repairs often must be instituted at virtually inaccessible locations. It is therefore extremely desirable to have standardization of parts so that replacement parts for repair can be flown to the damaged aircraft and incorporated therein without there being any worry about the part not being the proper size. One particular type item peculiarly susceptible to the problem of standardization are cylinders used in transmitting hydraulic pressure, such as for aircraft brakes. The fluid utilized in these cylinders occasionally gets contaminated with metallic particles and other foreign matter and the pistons within the cylinders grind the particles into the cylinder walls, causing wearing thereof. This wear destroys the seal between the piston and the cylinder wall, resulting in pressure leaks and eventual malfunction of the hydraulic system. It is therefore oftentimes necessary to repair the inner cylinder wall. This may be done in a variety of fashions. For example, the entire cylinder may be replaced. This is extremely undesirable as these cylinders may be exceedingly expensive, certain cylinders used in aircraft (brake) systems costing on the order of several thousands of dollars each. Another method of repair is to rebore and refinish the cylinder walls. A problem with this approach is that the diameter of the cylinder is increased by this method, necessitating the replacement of the original piston by an oversized piston. This latter procedure is unsatisfactory because the pistons are then not of standard size and the strength of the assembly is adversely affected. In order to overcome these disadvantages, the prior art has developed a process wherein the cylinder is rebored and material is plated or otherwise deposited on the inside of the cylinder to build up the inner walls and bring the diameter back down to the original diameter so that standard pistons may be utilized. This latter approach has disadvantages. For example, typical aircraft hydraulic cylinders are made of an aluminum alloy and the plating material has typically been hard chrome, nickel or other deposited materials. Because of the difference in coefficient of thermal expansion and ductility of the base material and the plated material, the plated walls have shown a tendency to crack. Another approach in the past has been to rebore the cylinder and press fit a sleeve therein, the inner diameter of the sleeve being the same as the original diameter of the cylinder. However, the hydraulic systems utilized in aircraft brake systems have extremely high fluid pressures, sometimes on the order of 3,000 pounds per square inch. This high pressure can actually drive the sleeve out of the cylinder. It is therefore desirable to have some way of repairing cylinders which overcomes all the disadvantages of the prior art approaches but still allows for the standardization of parts.